AR Finishes

So, not crazy about the Duracoat job on the AR build that I recently bought. Im pretty sure that it was just due to poor attention to detail/prep, however, I need to know:

-What types of finishes are out there?
-What was the OEM finish for this style rifle?
-What is the optimal finish for this type of rifle (durability, etc)?
And.most importantly, can anyone recommend a professional service provider from personal experience?